The present invention concerns vehicle suspension systems and particularly a device enhancing wheel-to-ground contact of a swing arm mounted wheel subject to severe, fluctuating loads.
In that type of motorcycle used in cross country riding and in motocross events the rear wheel is carried on what is termed a swing arm which moves about a forwardly located horizontal axis at that point of swing arm attachment to the motorcycle frame. Such swing arm mounting permits a wide range of rear wheel travel important to the rapid traversing of the rough terrain encountered at relatively high speeds. Also conventional is the installation of shock absorber units pivotally mounted at their lower rear ends to rearward portions of the yoke shaped swing arm with their upper or forwardly located ends in pivoted attachment to the motorcycle frame. Commonly, such shock absorber units exteriorly include coil springs which, in some cases, are adjustably mounted on the unit to permit pre-loading of the spring to best suit riding conditions.
In motocross competition it is not uncommon for suspension loading to cause the rear wheel to travel several inches relative to the frame and often to be momentarily out of ground contact. Obviously, during such periods no motive power is imparted to the motorcycle and further stability is jeopardized. Accordingly several inventive efforts have been made to control motion of a swing arm carried rear wheel with known efforts being found in the following recent U.S. Pat. Nos. 3,877,539; 3,948,543; 3,966,006; 3,977,697. While swing arm control may be enhanced by such efforts, the devices proposed have not found wide acceptance for one reason or another. The per unit cost of such devices and cost of necessary motorcycle modification bear directly on the adoption by the public of such proposed improvements. Further, some of the proposed improvements incur the disadvantage of substantially increasing vehicle weight and add appendages to the motorcycle which could come into contact with the terrain which, of course, is not only undesirable but may cause a fall with consequent risks to the operator.